What is X11?

X, also known as X11, is a windowing system for UNIX-like operating systems such as Linux. It came out in 1984 at MIT, but since 1987 the X.Org foundation have been leading the project. X uses a client-server model, enabling the forwarding of X client applications through a secure shell. Forwarding X through a shell can be useful for remotely accessing a system where a GUI is needed and due to the nature of OpenSSH it also encrypts the data packets.

X is just the very basic framework for building a graphical user interface environment, in which dedicated applications such as window managers can co-exist in.

Unlike earlier display systems that existed prior to X, the X window system was specifically designed to be used across network connections, rather than on an attached display device.

X11 utilises network transparency, which is a protocol’s ability to transmit data across a network in a way that it’s transparent, yet can’t be seen by the child applications that are using the X11 protocol parent process. This is similar to a technique found in cloud computing, where remote files can be presented to the user as locally accessible, but are actually stored in the cloud.

Another reason that the X11 protocol was designed with network access in mind is with the specific aim to perform computationally intensive tasks on a remote machine, and then see the results on a local desktop machine.